Modified oilseed materials are used as food additives for enhancing texture and other functional characteristics of various food products as well as a source of protein. The use of modified oilseed materials particularly modified soybean materials may be limited in some instances, however, due to their beany flavor and tan-like color. It is still unclear exactly which components are responsible for the flavor and color characteristics of oilseeds, though a variety of compounds are suspected of causing these characteristics. Among these are aliphatic carbonyls, phenolics, volatile fatty acids and amines, esters and alcohols.
There are extensive reports of processes used for the isolation, purification and improvement of the nutritional quality and flavor of oilseed materials, particularly soybean materials. Soybean protein in its native state is unpalatable and has impaired nutritional quality due to the presence of phytic acid complexes which interfere with mammalian mineral absorption, and the presence of antinutritional factors which interfere with protein digestion in mammals. The reported methods include the destruction of the trypsin inhibitors by heat treatment as well as methods for the removal of phytic acid. A wide variety of attempts to improve the yield of protein secured as purified isolate relative to that contained in the soybean raw material have also been described.
Many processes for improving soy protein flavor involve the application of heat, toasting, alcohol extraction and/or enzyme modification. These types of processes often result in substantial protein denaturation and modification, thereby substantially altering the product""s functionality. In addition, these processes can promote interactions between proteins with lipid and carbohydrate constituents and their decomposition products. These types of reactions can reduce the utility of soy proteins in food products, especially in those that require highly soluble and functional proteins, as in dairy foods and beverages.
Commercial soy protein concentrates, which are defined as soy protein products having at least 70% by weight protein (dry solids basis or xe2x80x9cdsbxe2x80x9d), are generally produced by removing soluble sugars, ash and some minor constituents. The sugars are commonly removed by extracting with: (1) aqueous alcohol; (2) dilute aqueous acid; or (3) water, after first insolubilizing the protein with moist heating. These processes generally produce soy protein products with a distinctive taste and color.
Soy protein isolates are defined as products having at least 90% by weight protein (dsb). Commercial processes for producing soy protein isolates are generally based on acid precipitation of protein. These methods of producing, typically include (1) extracting the protein from soy flakes with water at an alkaline pH and removing solids from the liquid extract; (2) subjecting the liquid extract to isoelectric precipitation by adjusting the pH of the liquid extract to the point of minimum protein solubility to obtain the maximum amount of protein precipitate; and (3) separating precipitated protein curd from by-product liquid whey. This type of process, however, still tends to produce a protein product with a distinctive taste and color.
A number of examples of processes for producing concentrated soy protein products using membrane filtration technology have been reported. Due to a number of factors including cost, efficiency and/or product characteristics, however, membrane-based purification approaches have never experienced widespread adoption as commercial processes. These processes can suffer from one or more disadvantages, such as reduced functional characteristics in the resulting protein product and/or the production of a product which has an xe2x80x9coffxe2x80x9d flavor and/or an off-color such as a dark cream to light tan color. Membrane-based processes can also be difficult to operate under commercial production conditions due to problems associated with bacterial contamination and fouling of the membranes. Bacterial contamination can have undesirable consequences for the flavor of the product.
Processed meat compositions, which include a modified oilseed material with desirable flavor and/or color characteristics derived from oilseed material, such as defatted soybean white flakes or soybean meal, are described herein. The present processed meat compositions, which include the modified oilseed material are particularly suitable for use as a protein source for human and/or animal consumption.
The present modified oilseed material can be produced by a membrane-based purification process which typically includes an extraction step to solubolize proteinaceous material present in an oilseed material. It may be desirable to conduct the extraction as a continuous, multistage process, e.g., a countercurrent extraction.
The modified oilseed material can commonly be produced by a process which includes an extraction step to solubilize proteinaceous material present in an oilseed material. The process uses one or more microporous membranes to separate and concentrate protein from the extract. It is generally advantageous to use a microporous membrane which has a filter surface with a relatively low contact angle, e.g., no more than about 40 degrees. The process commonly utilizes either relatively large pore ultrafiltration membranes (e.g., membranes with a molecular weight cut-off (xe2x80x9cMWCOxe2x80x9d) of about 25,000 to 500,000) or microfiltration membranes with pore sizes up to about 1.5. When microfiltration membranes are employed, those with pore sizes of no more than about 1.0xcexc and, more desirably, no more than about 0.5xcexc are particularly suitable. Herein, the term xe2x80x9cmicroporous membranexe2x80x9d is used to refer to ultrafiltration membranes and microfiltration membranes collectively. By employing such relatively large pore microporous membranes, the membrane filtration operation in the present process can be carried out using transmembrane pressures of no more than about 100 psig, desirably no more than about 50 psig, and more commonly in the range of 10-20 psig.
The modified oilseed material formed by the present method can be used to produce protein supplemented food products such as processed meat compositions. The modified oilseed material can have a variety of characteristics that make it suitable for use as a protein source for incorporation into food products. A suitable modified oilseed material may include at least about 85 wt. % (dsb) protein, preferably at least about 90 wt. % (dsb) protein, and have one or more of the following characteristics: a MW50 of at least about 200 kDa; at least about 40% of the material has an apparent molecular weight of greater than 300 kDa; at least about 40 wt. % of the protein in a 50 mg sample may be soluable in 1.0 mL water at 25xc2x0 C.; a turbidity factor of no more than about 0.95; a 13.5% aqueous solution forms a gel having a breaking strength of no more than about 25 g; an NSI of at least about 80; at least about 1.4% cysteine as a percentage of total protein; a Gardner L value of at least about 85; a substantially bland taste; a viscosity slope of at least about 10 cP/min; an EOR of no more than about 0.75 mL; a melting temperature of at least about 87xc2x0 C.; a latent heat of at least about 5 joules/g; a ratio of sodium ions to a total amount of sodium, calcium and potassium ions of no more than 0.5; no more than about 7000 mg/kg (dsb) sodium ions; and a bacteria load of no more than about 50,000 cfu/g.
A particularly desirable modified oilseed material formed by the present method which may be used to produce a protein supplemented food product may include at least about 85 wt. % (dsb) protein, preferably at least about 90 wt. % (dsb) protein, and meet one or more of the following criteria: a MW50 of at least about 400 kDa; at least about 60% of the material has an apparent molecular weight of greater than 300 kDa; at least about 40 wt. % of the protein in a 50 mg sample may be soluable in 1.0 mL water at 25xc2x0 C.; a turbidity factor of no more than about 0.95; a 13.5% aqueous solution forms a gel having a breaking strength of no more than about 25 g; an NSI of at least about 80; at least about 1.5% cysteine as a percentage of total protein; a Gardner L value of at least about 85; a substantially bland taste; a viscosity slope of at least about 50 cP/min; an EOR of no more than about 0.5 mL; a melting temperature of at least about 87xc2x0 C.; a latent heat of at least about 5 joules/g; a ratio of sodium ions to a total amount of sodium, calcium and potassium ions of no more than 0.5; no more than about 7000 mg/kg (dsb) sodium ions; and a bacteria load of no more than about 50,000 cfu/g.
The modified oilseed material used to supplement the present processed meat compositions generally has a high protein content as well being light colored and having desirable flavor characteristics. The modified oilseed material can have a variety of other characteristics that make it suitable for use as a protein source for incorporation into foods for human and/or animal consumption.
The modified oilseed material can commonly be produced by a process which includes an extraction step to solubilize proteinaceous material present in an oilseed material and a subsequent purification of the extract using one or more microporous membranes to remove carbohydrates, salts and other non-protein components. Very often, the extract is clarified prior to membrane purification by at least removing a substantial amount of the particulate material present in the suspension produced by the extraction procedure.
The process described herein uses one or more microporous membranes to separate and concentrate protein from an oilseed extract. It is generally advantageous to use a microporous membrane which has a filter surface with a relatively low contact angle, e.g., no more than about 40 degrees. Microporous membranes with even lower contact angles, e.g., with filter surfaces having a contact angle of no more than about 30 degrees and in some instances of no more than about 15 degrees, are particularly suitable for use in the present method. The process commonly utilizes either relatively large pore ultrafiltration membranes (e.g., membranes with a molecular weight cut-off (xe2x80x9cMWCOxe2x80x9d) of at least about 30,000) or microfiltration membranes with pore sizes up to about 2xcexc.
Source of Oilseed Material
The starting material employed in the present method generally includes material derived from defatted oilseed material, although other forms of oilseed based material may be employed. The fat may be substantially removed from dehusked oilseeds by a number of different methods, e.g., by simply pressing the dehusked seeds or by extracting the dehusked seeds with an organic solvent, such as hexane. The defatted oilseed material which is employed in preferred embodiments of the present process typically contains no more than about 3 wt. % and, preferably, no more than about 1 wt. % fat. The solvent extraction process is typically conducted on dehusked oilseeds that have been flattened into flakes. The product of such an extraction is referred to as an oilseed xe2x80x9cwhite flake.xe2x80x9d For example, soybean white flake is generally obtained by pressing dehusked soybeans into a flat flake and removing a substantial portion of the residual oil content from the flakes by extraction with hexane. The residual solvent can be removed from the resulting white flake by a number of methods. In one procedure, the solvent is extracted by passing the oilseed white flake through a chamber containing hot solvent vapor. Residual hexane can then be removed from soybean white flakes by passage through a chamber containing hexane vapor at a temperature of at least about 75xc2x0 C. Under such conditions, the bulk of the residual hexane is volatilized from the flakes and can subsequently be removed, e.g., via vacuum. The material produced by this procedure is referred to as flash desolventized oilseed white flake. The flash desolventized oilseed white flake is then typically ground to produce a granular material (meal). If desired, however, the flash desolventized oilseed white flake may be used directly in the present method.
Another defatted oilseed derived material which is suitable for use in the present process is derived from material obtained by removing the hexane from the oilseed white flake by a process referred to as toasting. In this process, the hexane extracted oilseed white flakes are passed through a chamber containing steam at a temperature of at least about 105xc2x0 C. This causes the solvent in the flakes to volatilize and be carried away with the steam. The resulting product is referred to as toasted oilseed flake. As with flash desolventized oilseed white flake, toasted oilseed flake may be used directly in the present method or may be ground into a granular material prior to extraction.
While the desolventized oilseed white flake may be used directly in the extraction step, more commonly the desolventized flake is ground to a meal prior to being employed as starting material for the extraction. Oilseed meals of this type, such as soybean meal, are used in a wide variety of other applications and are readily available from commercial sources. Other examples of oilseed materials which are suitable for use in the culture medium include canola meal, sunflower meal, cottonseed meal, peanut meal, lupin meal and mixtures thereof. Oilseed materials derived from defatted soybean and/or defatted cottonseed are particularly suitable for use in the present method since such materials have a relatively high protein content. It is important to note that although many of the examples and descriptions herein are applied to a modified soybean material, the present method and material should not be construed to be so limited, and may be applied to other grains and oilseeds.
Extraction of Oilseed Material
The extraction of the protein fraction from oilseed material can be carried out under a variety of conditions using conventional equipment. Among the factors which affect the choice of process parameters and equipment are the efficiency of the extraction, effects on the quality of the protein in the extract and minimization of the environmental impact of the process. For cost and environmental reasons, one often would like to reduce the volume of water used in the process. The process parameters are also generally selected so as to minimize the degradation of protein, e.g., via indigenous enzymes and/or chemical reactions, as well as to avoid substantial bacterial contamination of the extract.
A variety of reactor configurations including stirred tank reactors, fluidized bed reactors, packed bed reactors may be employed in the extraction step. For example, the entire extraction reaction may be performed in a single vessel having appropriate mechanisms to control the temperature and mixing of the medium. Alternatively, the extraction may be carried out in multiple stages performed in separate reaction vessels.
As is common with many processes, the optimization of the various objectives typically requires a balancing in the choice of process parameters. For example, in order to avoid substantial chemical degradation of the protein, the extraction may be run at a relatively low temperature, e.g., about 15xc2x0 C. to 40xc2x0 C. and preferably about 20xc2x0 C. to 35xc2x0 C. Such temperatures, however, can be quite conducive to bacterial growth so that it may be best to minimize extraction times and/or conduct subsequent process operations at higher temperatures to reduce bacterial growth.
Alternately, the extraction may be run at slightly higher temperatures, e.g., 50xc2x0 C. to 60xc2x0 C., to reduce the chances of bacterial contamination. While this can reduce bacterial growth, the increased temperature can exacerbate potential problems due to chemical degradation of proteinaceous material. Thus, as for the extraction run at closer to room temperature, when the extraction is carried out at 50xc2x0 C. to 60xc2x0 C., it is generally desirable to complete the extraction as rapidly as possible in order minimize degradation of protein. When the extraction is run at temperatures between about 20xc2x0 C. and 60xc2x0 C., it has generally been found that extraction times of one to two hours are sufficient to allow high recoveries of protein while avoiding significant protein degradation and/or bacterial contamination. When higher temperatures are used, e.g., 50xc2x0 C. to 60xc2x0 C., it has been found that the extraction times of no more than about thirty minutes are commonly sufficient to allow high recoveries of protein while avoiding significant protein degradation and/or bacterial contamination. Use of higher temperatures is generally avoided since substantial exposure to temperatures of 60xc2x0 C. and above can lead to protein solutions which have a tendency to gel during processing.
Although oilseed materials have been extracted under both acidic and basic conditions to obtain their proteinaceous material, the present method typically includes an extraction under basic conditions, e.g., using an alkaline solution having a pH of about 7.5 to about 10. Very often, the extraction is conducted by contacting the oilseed material with an aqueous solution containing a set amount of base, such as sodium hydroxide, potassium hydroxide, ammonium hydroxide and/or calcium hydroxide, and allowing the pH to slowly decrease as the base is neutralized by substances extracted out of the solid oilseed material. The initial amount of base is typically chosen so that at the end of the extraction operation the extract has a desired pH value, e.g., a pH within the range of 8.0 to 9.5. Alternately, the pH of the aqueous phase can be monitored (continuously or at periodic time intervals) during the extraction and base can be added as needed to maintain the pH at a desired value.
When the extraction is carried out as a single stage operation, the spent oilseed material is generally washed at least once with water or alkaline solution to recover proteinaceous material which may have been entrained in the solids fraction. The washings may either be combined with the main extract for further processing or may be used in the extraction of a subsequent batch of oilseed material.
The extraction operation commonly produces a mixture of insoluble material in an aqueous phase which includes soluble proteinaceous material. The extract may be subjected directly to separation via membrane filtration. In most cases, however, the extract is first clarified by removing at least a portion of the particulate matter from the mixture to form a clarified extract. Commonly, the clarification operation removes a significant portion and, preferably, substantially all of the particulate material. Clarification of the extract can enhance the efficiency of the subsequent membrane filtration operation and help avoid fouling problems with the membranes used in that operation.
The clarification can be carried out via filtration and/or a related process (e.g., centrifugation) commonly employed to remove particulate materials from the aqueous suspensions. Such processes do not, however, generally remove much of the soluble materials and thus the solubilized protein remains in the aqueous phase for further purification via membrane filtration. Because of the desire to achieve a high overall protein yield, the clarification step typically does not make use of filtration aids such as flocculants which could adsorb soluble proteinaceous material.
One suitable method of conducting the extraction and clarification operations employs a series of extraction tanks and decanter centrifuges to carry out a multi-stage counter current extraction process. This type of system permits highly efficient extractions to be carried out with a relatively low water to flake ratio. For example, this type of system can efficiently carry out extractions where the weight ratio of the aqueous extraction solution to the oilseed material in each phase is in the range of 6:1 to 10:1. Use of low water to flake ratios can enable the production of an oilseed extract which contains a relatively high concentration of dissolved solids, e.g., dissolved solids concentrations of 5 wt. % or higher and the production of extracts with at least about 7 wt. % solids is not uncommon. The use of low water to flake ratios and more concentrated extracts allows the process to be run in a system with lower volume capacity requirements, thereby decreasing demands on capital costs associated with the system.
If the system requirements in a particular instance do not include significant restrictions on overall volume, the extraction process may be carried using higher water to flake ratios. Where relatively high water to flake ratios are employed in the extraction operation, e.g., ratios of 20:1 to 40:1, it may be more convenient to carry out the extraction in a single stage. While these types of water to flake ratios will require systems capable of handling larger volumes of fluids (per pound of starting oilseed material), the higher dilution factor in the protein extraction can decrease the potential for fouling the microporous membrane(s) used in the membrane filtration operation.
Membrane Filtration
Extract liquor is transferred from the extraction system to a membrane separation system, generally by first introducing clarified extract into a membrane feed tank. The extract liquor commonly contains about 4.0-5.0% soluble protein and about 1.5-2.0% dissolved non-protein material. One purpose of the microfiltration operation is to separate protein from non-protein material. This can be accomplished by circulating the extract liquor through a set of microfiltration membranes. Water and the non-protein materials pass through the membrane as permeate while most of the protein is retained in the circulating stream (xe2x80x9cretentatexe2x80x9d). The protein-containing retentate is typically allowed to concentrate by about a 2.5-3xc3x97 factor (e.g., concentration of 30 gallons of incoming crude extract by a 3xc3x97 factor produces 10 gallons of retentate). The concentration factor can be conveniently monitored by measure the volume of permeate passing through the membranes. Membrane concentration of the extract by a 3xc3x97 X factor generally produces a retentate stream with dissolved solids containing at least about 80 wt. % protein (dsb). In order to increase the protein concentration to 90 wt. %, two 1:1 diafiltrations are typically carried out. In a diafiltration operation, water is added to the concentrated retentate and then removed through the microporous membranes. This can be carried out in the manner described above or, in an alternate embodiment of the present method, the diafiltration can be carried out at the initial stage of the membrane filtration, e.g., by continuously adding water to the incoming extract in a feed tank so as to substantially maintain the original volume.
The membrane filtration operation typically produces a retentate which is concentrated by at least a 2.5xc3x97 factor, i.e., passing a volume of the extract through the filtration system produces a protein-enriched retentate having a volume of no more than about 40% of the original extract volume. The output from the membrane filtration operation generally provides a protein-enriched retentate which includes at least about 10 wt. % protein, and protein concentrations of 12 to 14 wt. % are readily attained.
For environmental and efficiency reasons, it is generally desirable to recover as much of the water from the membrane permeates as possible and recycle the recovered water back into the process. This decreases the overall hydraulic demand of the process as well as minimizing the volume of effluent discharged by the process. Typically, the diafiltration permeate is combined with the permeate from the concentration phase of the membrane filtration. The bulk of the water in the combined permeate can be recovered by separating the combined permeate with a reverse osmosis (xe2x80x9cROxe2x80x9d) membrane into an RO retentate and an RO permeate. RO separation can produce a permeate that is essentially pure water. This can be recycled back into earlier stages of the process. For example, the RO permeate can be used in an aqueous solution for extracting the oilseed material. The RO permeate can also be utilized in a diafiltration operation by diluting protein-enriched retentate with an aqueous diluent which includes the RO permeate.
The present process uses a membrane filtration system with one or more microporous membranes to separate and concentrate protein from the extract. It is generally advantageous to use a microporous membrane which has a filter surface with a relatively low contact angle, e.g., no more than about 40 degrees, as such membranes can provide efficient separation while exhibiting good resistance to fouling. Microporous membranes with even lower filter surface contact angles (i.e., surfaces having greater hydrophilicity) are particularly suitable for use in the present process. Such membranes may have a filter surface with a contact angle of 25 degrees or less and some membranes may have a filter surface contact angle of no more than about 10 degrees.
As used herein, the term xe2x80x9ccontact anglexe2x80x9d refers to contact angles of surfaces measured using the Sessile Drop Method. This is an optical contact angle method used to estimate the wetting property of a localized region on a surface. The angle between the baseline of a drop of water (applied to a flat membrane surface using a syringe) and the tangent at the drop boundary is measured. An example of a suitable instrument for measuring contact angles is a model DSA 10 Drop Shape Analysis System commercially available from Kruss.
The membranes should be capable of retaining a high percentage of the medium and high molecular weight protein components present in the extract while allowing water and other components to pass through the membrane. The membrane filtration operation commonly utilizes either relatively large pore ultrafiltration membranes (e.g., membranes with a molecular weight cut-off (xe2x80x9cMWCOxe2x80x9d) of at least about 30,000) or microfiltration membranes with pore sizes up to about 1.5xcexc. Low contact angle microfiltration membranes with MWCOs of 25,000 to 200,000 are particularly suitable for use in the present process. Particular examples of suitable microporous membranes in modified PAN membranes with a filter surface contact angle of no more than about 25 degrees and an MWCO of 30,000 to 100,000. To be useful in commercial versions of the process, the membranes should be capable of maintaining substantial permeation rates, e.g., allowing roughly 1500 to 3000 mL/min to pass through a membrane module containing circa 12 sq. meters of membrane surface area. By employing such relatively large pore microporous membranes, the membrane filtration operation can generally be carried out using membrane back pressures of no more than about 100 psig. More preferably the membrane back pressure is no more than about 50 psig and efficient membrane separation has been achieved with back pressures in the range of 10-20 psig.
The membrane filtration system is generally configured to run in a cross-flow filtration mode. Because larger particles and debris are typically removed by the earlier clarification operation, the microporous membrane tends not to become clogged easily. Inclusion of the clarification step upstream in the process tends to result in longer membrane life and higher flux rates through the membrane. The membrane filtration system typically employs one or more interchangeable membrane modules. This allows membrane pore size (or MWCO) and/or membrane type to be altered as needed and allows easy replacement of fouled membranes.
Cross-flow filtrations can be run either continuously or in batch mode. Cross-flow membrane filtration can be run in a variety of flow configurations. For example, a tubular configuration, in which the membranes are arranged longitudinally in tubes similar to the tubes in a shell and tube heat exchanger, is one common configuration since it allows processing of solutions which include a variety of particle sizes. A number of other conventional cross-flow configurations, e.g., flat sheet and spiral wound, are known to provide effective membrane separations while reducing fouling of the membrane. Spiral wound cross-flow membrane systems are particularly suitable for use in the present processes, especially where the feed solution contains relatively little particulate matter, such as a clarified oilseed extract. Spiral wound membrane modules tend to provide highly efficient separations and permit the design of filtration systems with large membrane surface areas in a relatively compact space.
As with the extraction operation, the temperature of the protein-containing solution during the membrane filtration operation can affect the chemical state of the protein (e.g., via degradation and/or denaturation) as well as the amount of bacterial contamination which occurs. Lower temperatures tend to minimize chemical degradation of the protein. However, at lower temperatures bacterial growth can be a problem and the viscosity of more concentrated protein solutions (e.g., solutions with at least about 10 wt. % protein) can present processing problems. The present inventors have found that maintaining the protein-containing extract at about 55 to 60xc2x0 C. while conducting the membrane separation can effectively suppress bacterial growth while minimizing changes in protein functionality due to chemical degradation/denaturation. It appears that any substantial exposure to higher temperatures can cause changes in the protein which can make concentrated solutions more prone to gelling, e.g., during a subsequent spray drying operation.
When the membrane filtration is run as a batch operation, the membranes are generally cleaned in between each run. Typically the membrane system will have been cleaned and sanitized the day before a run and the membranes will be stored in a sodium hypochlorite solution. Before use, the membrane system the hypochlorite solution is then drained out of the membrane system and the entire system is rinsed with water. When the membrane separation is carried out as a continuous operation, the membranes are commonly shut down at periodic intervals and cleaned in a similar fashion.
A variety of methods are known for cleaning and sanitizing microporous membrane systems during ongoing use. One suitable cleaning procedure includes sequentially flushing the membrane with a series of basic, acidic and sanitizing solutions. Examples of suitable sanitizing solutions include sodium hypochlorite solutions, peroxide solutions, and surfactant-based aqueous sanitizing solution. Typically, the membrane is rinsed with water between treatments with the various cleaning solutions. For example, it has been found that membranes with a low contact angle filtering surface (e.g., modified PAN microporous membranes) can be effectively cleaned by being flushed with the following sequence of solutions:
1) Water;
2) Caustic solution (e.g., 0.2 wt. % NaOH solution);
3) Water;
4) Mild acid solution (e.g., aqueous solution with a pH 5.5-6);
5) Surfactant-based aqueous sanitizing solution (Ultra-Clean(trademark); available from Ecolab, St. Paul, Minn.); and
6) Water.
The cleaning sequence is commonly carried out using room temperature solutions. If the membrane is significantly fouled, it may be necessary to carry out one or more of the rinsing steps at an elevated temperature, e.g., by conducting the caustic, acidic and/or sanitizing rinse at a temperature of about 40xc2x0 C. to 50xc2x0 C. In some instances, the effectiveness of the cleaning sequence can be enhanced by using a more strongly acidic rinse, e.g., by rinsing the membrane with a acidic solution having a pH of about 4 to 5. Other types of solutions can be used as a sanitizing solution. For example, if the membrane is sufficiently chemically inert, an oxidizing solution (e.g., a dilute solution of NaOCl or a dilute hydrogen peroxide solution) can be used as a sanitizing agent. After the final water rinse in the cleaning sequence, the membrane can be used immediately to effect the membrane separation of the present process. Alternatively, the membrane can be stored after cleaning. It is common to store the cleaned membrane in contact with a dilute bleach solution and then rinse the membrane again with water just prior to use.
By selecting a membrane which can be effectively cleaned (e.g., a membrane with low contact angle filtering surface such as a modified PAN membrane) it is possible to carry out membrane filtration of concentrated oilseed protein extracts which produce retentates having relatively low bacterial levels. For example, by employing a modified PAN membrane and a cleaning procedure similar to that outlined above, it is possible to produce spray dried protein concentrates having a total bacterial plate count of no more than about 300,000 cfu/g and, desirably, no more than about 50,000 cfu/g without subjecting the retentate to pasteurization (e.g., via HTST treatment).
Downstream Processing of Retentate
The retentate produced by the membrane filtration operation is often pasteurized to ensure that microbial activity is minimized. The pasteurization generally entails raising the internal temperature of the retentate to about 75xc2x0 C. or above and maintaining that temperature for a sufficient amount of time to kill most of the bacteria present in the solution, e.g., by holding the solution at 75xc2x0 C. for about 10-15 minutes. The product commonly is pasteurized by subjecting the concentrated retentate to xe2x80x9cHTSTxe2x80x9d treatment. The HTST treatment can be carried out by pumping the concentrate retentate through a steam injector where the protein-containing concentrate is mixed with live steam and can be heated rapidly to about 80-85xc2x0 C. (circa 180xc2x0 F.). The heated concentrate is then typically passed through a hold tube, under pressure, for a relatively short period of time, e.g., 5 to 10 seconds. After the hold tube, the heated retentate can be cooled by passage into to a vacuum vessel. The evaporation of water from the retentate under vacuum results in flash cooling of the heated solution, allowing the temperature to be rapidly dropped to the range of 45-50xc2x0 C. (circa 130-140xc2x0 F.). This type of treatment has been found to be very effective at destroying bacteria while avoiding substantial chemical degradation of the protein.
To improve its storage properties, the modified oilseed product is typically dried such that the product contains no more than about 12 wt. % moisture, and preferably, no more than about 8 wt. % moisture, based upon the weight of the final dried product. Depending on the drying method utilized and the form of the dried product, after drying the product may be ground into free-flowing solid particles in order to facilitate handling and packaging. For example, if the dried, modified oilseed product is dried into a cake, it can be ground into a dried powder, preferably such that at least about 95 wt. % of the material is in the form of particles having a size of no more than about 10 mesh.
In an alternate process, after pH adjustment to a neutral pH, the liquid retentate may be spray dried to form a dry powdered product. The spray dried product is preferably dried to a water content of no more than about 10 wt. % water and, more preferably, about 4-6 wt. % water. The retentate can be spray dried by passing a concentrated solution (e.g., circa 10-15 wt. % solids) of the retentate through a spray dryer with a dryer inlet temperature of about 160-165xc2x0 C., a feed pump pressure of about 1500 psig and a discharge air temperature of about 90-95xc2x0 C.
Before the heating which can occur as part of either the spray drying or HTST treatment, it is usually advantageous to adjust the pH of the sample to about neutral. For example, the pH of the retentate is often adjusted to between 6.5 to 7.5 and, preferably between 6.7 and 7.2 prior to any further treatment which involves heating the sample. Heating the concentrated retentate can alter the molecular weight profile and consequently the functionality of the product. Compare, for example, the molecular weight profile of the product of Example 2 which was not heat treated with that of the product produced according to Example 1. The heat treated material contains a number of proteins not present its heated treated counterpart, the product of Example 1. The DSC""s of these two samples also show a distinct difference. The material produced according to Example 2 shows a relatively sharp, symmetrical peak at about 93xc2x0 C. The other material which was not heat treated, that of Example 4, also shows a strong absorption of energy at about 93xc2x0 C. All of the commercial products show either no absorption peak at all or small relatively weak absorption peak at about 82xc2x0 C. DSC scans of the two heat treated products formed by the present method (Examples 1 and 3) also only show a relatively weak absorption peak at about 82xc2x0 C.
In some instances, it may be advantageous to concentrate the retentate produced by the membrane filtration operation prior to a final spray drying step. This can be accomplished using conventional evaporative techniques, generally with the aid of vacuum to avoid extensive heating of the processed soy protein material. Where a concentration step of this type is included in the process, it normally occurs after the pH of the retentate has been adjusted to a neutral pH (e.g., a pH of roughly 6.8-7.0).
Characteristics of Modified Oilseed Material
The modified oilseed material can be derived from a variety of precursor oilseed materials, such as soybean meal, canola meal, sunflower meal, cottonseed meal, peanut meal, lupin meal or mixtures thereof. Soy bean flake or meal are particularly suitable sources of oilseed protein to utilize in the present method. The modified oilseed material can have a variety of characteristics that make it suitable for use as a protein source for incorporation into foods for human and/or animal consumption.
The modified oilseed material can be used to produce protein supplemented food products for human consumption. Examples of protein supplemented food products include beverages, processed meats, frozen desserts, confectionery products, dairy-type products, sauce compositions, and cereal grain products. The amount of modified oilseed material used to supplement a food product can vary greatly depending on the particular food product. A typical protein supplemented food product may have between 0.1 and 10 wt. %. The modified oilseed material may be used to produce additional food products. It is also important to note that the food products may be grouped into different or additional food categories. A specific food product may fall into more than one category (e.g., ice cream may be considered both a frozen dessert and a dairy-type product). The food products provided herein are for illustrative purposes only and are not meant to be an exhaustive list.
Examples of protein supplemented meat products include ground chicken products, water-added ham products, bologna, hot dogs, franks, chicken patties, chicken nuggets, beef patties, fish patties, surimi, bacon, luncheon meat, sandwich fillings, deli meats, meat snacks, meatballs, jerky, fajitas, bacon bits, injected meats, and bratwurst.
Consideration of the characteristics of the modified oilseed material is often important in developing a particular protein supplemented food product. For example, dispersability can facilitate easy mixing of the ingredients (whether a dry formulated mix or the dry isolates) into water, ideally leading to a relatively stable homogenous suspension. Solubility may be desired to reduce the amount of particulates that can be found in finished beverages. Suspendability may be desired to prevent the settling of the insoluble components from the finished formula upon standing. Generally, a white colored modified oilseed material is preferred as tan and brown solutions can be difficult to color into white (milk-like) or brightly colored (fruit-like) colors. Clarity of modified oilseed material in solution can also be an important beverage characteristic. Foaming, although usually undesired in beverages as it can complicate mixing, can also be a positive characteristic in some products (e.g., milk shake-like products). Other characteristics that can be important for particular food compositions include molecular weight, gelling capability, viscosity, emulsion stability fact content and amino acid content. Specific properties according to one or more of these characteristics may be advantageous in developing protein supplemented food products.
The primary function of soy protein isolates (xe2x80x9cSPIxe2x80x9d) in processed meats is in holding water and fat through the cooking process (increasing yield) then preventing water loss during storage (decreasing purge). This must be done while maintaining the texture, flavor and aroma of the finished product.
The modified oilseed material formed by the present method typically includes a high percentage of high molecular weight proteins and is less contaminated with low molecular weight proteins. A suitable method to analyze the content of high molecular weight proteins found in the material is based on chromatographic data as described in Example 16.
The raw chromatogramic data may be used to calculate a number of different metrics. One metric is to calculate the molecular weight at which 50% of the mass is above and 50% of the mass is below. This first metric is not precisely the mean molecular weight, but is closer to a weighted average molecular weight. This is referred to herein by the term xe2x80x9cMW50.xe2x80x9d Another metric is to calculate the wt. % of modified oilseed material that has an apparent molecular weight that is greater than 300 kDa. Yet another metric is to calculate the wt. % of modified oilseed material that has an apparent molecular weight that is less than 100 kDa. Any one of these three metrics may be used individually to characterize the molecular weight of a particular modified oilseed material. Alternatively, combinations of two or more of these metrics may be used to characterize the molecular weight profile of a modified oilseed material.
Preferably, the modified oilseed material formed by the present method has a MW50 of at least about 200 kDa. More preferably, at least about 400 kDa. Modified oilseed material that has a MW50 of at least about 600 kDa can be particularly suitable for some applications. As for the second metric mentioned above, at least about 40% of a suitable modified oilseed material may have an apparent molecular weight of greater than 300 kDa. For some applications, it may be desirable if at least about 60% of the modified oilseed material has an apparent molecular weight of greater than 300 kDa. According to the third metric mentioned above, preferably no more than about 40% of the modified oilseed material has an apparent molecular weight of less than 100 kDa. For some applications, however, preferably no more than about 35% of the modified oilseed material has an apparent molecular weight of less than 100 kDa. A suitable modified oilseed material may meet the preferred values of one or more of these three metrics. For example, a particularly suitable modified oilseed material may have a MW50 of at least about 200 kDa and at least about 60% of the modified oilseed material has an apparent molecular weight of greater than 300 kDa. Modified oilseed material that has a MW50 at least about 600 kDa and at least about 60% of the modified oilseed material has an apparent molecular weight of greater than 300 kDa can be formed by the present method.
The modified oilseed material formed by the present method typically includes a protein fraction with good solubility. For example, modified oilseed material where at least about 40 wt. % of the protein in a 50 mg sample of the material is soluble in 1.0 mL water at 25xc2x0 C. can be formed by the present method. Samples in which at least about 50 wt. % of the protein is soluble under these conditions are attainable. The solubility of a modified oilseed material can also be described by its NSI as discussed in Example 9.
In addition to having relatively good solubility, the modified oilseed material formed by the present method often has good properties with respect to its suspendability in aqueous solutions. For example, the present process can be used to provide modified oilseed material which has good suspendability. One measure of the suspendability of a dried oilseed protein product is its xe2x80x9cturbidity factor.xe2x80x9d As used herein, the xe2x80x9cturbidity factorxe2x80x9d is defined in terms of the assay described in Example 14. As described in this example, sufficient sample to make a 5 wt. % solution is dissolved/dispersed in a 5 wt. % sucrose solution. After standing for about 1 hour at room temperature, an aliquot of the slurry is diluted 10-fold into water and the absorbance at 500 nm was measured. This absorbance measurement at 500 nm (referred to herein as the xe2x80x9cturbidity factorxe2x80x9d) is a measure of turbidity with higher absorbance values indicating higher turbidity and lower solubility.
Preferably, the modified oilseed material formed by the present method has an absorbance at 500 nm of no more than about 0.95 in this assay, i.e., a turbidity factor of no more than about 0.95. Stated otherwise, a dispersion of 0.5 wt. % of the dried oilseed protein product in a 0.5 wt. % aqueous sucrose solution has an absorbance at 500 nm of no more than about 0.95 (after standing for about one hour as a 5 wt. % solution in a 5 wt. % sucrose solution).
The present method allows the production of modified oilseed materials which have desirable color characteristics. The products generally have a very light color as evidenced by their Gardner L values. For example, the present method allows the preparation of modified oilseed materials which have a dry Gardner L value of at least about 85. In some instances, e.g., by running the extraction at a weakly alkaline pH of 8-9 and conducting the initial extraction at a relatively low temperature (circa 25-35xc2x0 C.; 75-95xc2x0 F.), it may be possible to produce a sample of an oilseed protein isolate which has a Gardner L value (dry) of at least about 88.
The present method further allows the production of modified oilseed material which has desirable flavor characteristics. An undesirable flavor is often one of the biggest hindrances to the use of modified oilseed material in a consumer product. The flavor of modified oilseed material, especially modified soy protein, is derived from a complex mixture of components. For example, bitterness and other off flavors are often caused by the presence of low molecular weight peptides (400 less than MW less than 2000) and volatile compounds. Some of these small molecules arise in the oilseed itself and others are bound to the modified oilseed material at various points in the production process. The substantially bland taste which is typical of the modified oilseed materials formed by the present method, may be due to fewer small molecular weight peptides and volatile compounds.
For some food related applications the ability of a modified oilseed material to form a gel can be an important functional characteristic. In gelling, the protein denatures to form a loose network of protein surrounding and binding a large amount of water. As used herein, the term xe2x80x9cgel strengthxe2x80x9d refers to the breaking strength of a 12.5 wt. % aqueous solution of the modified oilseed material after setting and equilibrating the gel at refrigerator temperature (circa 4-5xc2x0 C.). Modified oilseed materials formed by the present method may have a gel strength of no more than about 25 g.
The modified oilseed material formed by the present method typically demonstrate desirable viscosity properties. A modified oilseed material that provides a thinner solution under one set of parameters is advantageous in applications like meat injection where thinner solutions can more easily be injected or massaged into meat products. Typically, a modified oilseed material that does not show thinning upon heating is generally preferred. For some applications, it is a desirable property to be able to maintain viscosity through heating cycles. The modified oilseed material formed by the present method increases viscosity with heating so its hold on water is improving during the early stage of cooking. In contrast, most commercial samples decrease in viscosity early in cooking and decrease their hold on the water.
Upon heating, protein molecules vibrate more vigorously and bind more water. At some point, the molecules lose their native conformation and become totally exposed to the water. This is called gelatinization in starch and denaturation in proteins. Further heating can decrease viscosity as all interactions between molecules are disrupted. Upon cooling, both types of polymers can form networks with high viscosity (called gels). For some food related applications the ability of a modified oilseed material to form a gel can be an important functional characteristic. Rapid viscosity analysis (xe2x80x9cRVAxe2x80x9d) was developed for analysis of starchy samples and is generally similar to Braebender analysis. Given the analogy between starch and protein systems, one can apply the RVA analysis described in Example 11 to the modified oilseed materials formed by the present method.
According to the method described in Example 11, one can measure the slope of the viscosity line over the temperature increase from 45xc2x0 C. to 95xc2x0 C., herein referred to as the xe2x80x9cviscosity slope.xe2x80x9d A suitable modified oilseed material may have a viscosity slope of at least about 30. A particularly suitable modified oilseed material may have a viscosity slope of at least about 50. As shown in Table 3, modified oilseed materials formed by the present method showed a viscosity slope of at least about 70.
For some food related applications the ability of a modified oilseed material to form an emulsion can be an important functional characteristic. Oil and water are not miscible and in the absence of a material to stabilize the interface between them, the total surface area of the interface will be minimized. This typically leads to separate oil and water phases. Proteins can stabilize these interfaces by denaturing onto the surface providing a coating to a droplet (whether of oil or water). The protein can interact with both the oil and the water and, in effect, insulate each from the other. Large molecular weight proteins are believed to be more able to denature onto such a droplet surface and provide greater stability than small proteins and thereby prevent droplet coalescence.
Emulsion stability may be determined based according to the procedure described in Example 12. According to this procedure, a sample is analyzed according to the amount of oil released from the emulsion. As used herein, the term xe2x80x9cEmulsion Oil Release,xe2x80x9d or xe2x80x9cEORxe2x80x9d refers to the amount of oil released (in mL) from the emulsion according to the conditions of the assay described in Example 12. Modified oilseed protein products prepared by the present method commonly form relatively stable emulsions. Typically, in the absence of centrifugation essentially no oil will separate from the emulsions within 2-3 hours. After the centrifugation procedure described in Example 12, a suitable material may have an EOR of no more than about 0.75 mL. Stated otherwise no more than about 0.75 mL of oil may be released from the emulsion. A particularly suitable emulsion may have an EOR of no more than about 0.5 mL, and more desirably, no more than about 0.3 mL after centrifugation.
During the membrane purification operation, while the levels of some components of the modified oilseed material are altered considerably, the fat content (measured after acid hydrolysis) in the present modified oilseed material remains relatively unchanged. Thus, if the oilseed material is substantially made up of material derived from defatted soybean flakes, the modified product obtained from the present process typically has a fat content of about 1 to 3 wt. % (dsb). For example, processing of defatted oilseed material, such as soybean meal, by the present method can produce a modified oilseed product having a protein content of 90 wt. % (dsb) or greater with no more than about 3 wt. % (dsb) and preferably, no more than about 2 wt. % fat. As used herein, the term xe2x80x9cfatxe2x80x9d refers to triacylglycerols and phospholipids.
The amino acid composition of a modified oilseed material may not only be important from a nutritional perspective, but it may also be an important part of determining the functional behavior of the protein. The amino acid content of a modified oilseed material may be determined by a variety of known methods depending on the particular amino acid in question. For example, cysteine may be analyzed after hydrolysis with performic acid according to known methods. To compare materials with different protein contents, compositions may be recalculated to a 100% protein basis. Typically, one would expect the amino acid composition of materials derived from a common starting material to be very similar. However, direct comparison of the average compositions shows that the modified oilseed materials formed by the present method includes more cysteine (assayed as cystine) than the commercial samples tested. For example, a suitable modified oilseed material may include at least about 1.35 wt. % cysteine as a percentage of total protein. A particularly suitable material may include at least about 1.5 wt. % cysteine as a percentage of total protein.
Cysteine can play an important role in nutrition and is one of the 10 essential amino acids. Cysteine may also play a role in the stabilization of the native structure of soy proteins. If oxidation-reduction reagents are used to xe2x80x9crestructurexe2x80x9d soy proteins, the cysteines may be damaged as an unintended consequence. Loss of native structure might remove some of the protection of the cysteine, making damage to the native structure more likely. As shown in Example 18, commercial materials show a substantial loss of native structure as measured by molecular weight and differential scanning calorimetry.
The modified oilseed material formed by the present method can have a variety of characteristics that make it suitable for use as a protein source for incorporation into food products for human and/or animal consumption. A suitable modified oilseed material may include at least about 85 wt. % (dsb) protein, preferably at least about 90 wt. % (dsb) protein. A suitable modified oilseed material may also have a MW50 of at least about 200 kDa and/or at least about 40% of the material has an apparent molecular weight of greater than 300 kDa. The modified oilseed material may also have one or more of the following characteristics: at least about 40 wt. % of the protein in a 50 mg sample may be soluable in 1.0 mL water at 25xc2x0 C.; a turbidity factor of no more than about 0.95; a 13.5% aqueous solution forms a gel having a breaking strength of no more than about 25 g; an NSI of at least about 80; at least about 1.4% cysteine as a percentage of total protein; a Gardner L value of at least about 85; a substantially bland taste; a viscosity slope of at least about 10 cP/min; an EOR of no more than about 0.75 mL; a melting temperature of at least about 87xc2x0 C.; a latent heat of at least about 5 joules/g; a ratio of sodium ions to a total amount of sodium, calcium and potassium ions of no more than 0.5; no more than about 7000 mg/kg (dsb) sodium ions; and a bacteria load of no more than about 50,000 cfu/g.
A particularly desirable modified oilseed material formed by the present method which may be used to produce a protein supplemented food product may include at least about 85 wt. % (dsb) protein, preferably at least about 90 wt. % (dsb) protein, and meet one or more of the following criteria: a MW50 of at least about 400 kDa; at least about 60% of the material has an apparent molecular weight of greater than 300 kDa; at least about 40 wt. % of the protein in a 50 mg sample may be soluable in 1.0 mL water at 25xc2x0 C.; a turbidity factor of no more than about 0.95; a 13.5% aqueous solution forms a gel having a breaking strength of no more than about 25 g; an NSI of at least about 80; at least about 1.5% cysteine as a percentage of total protein; a Gardner L value of at least about 85; a substantially bland taste; a viscosity slope of at least about 50 cP/min; an EOR of no more than about 0.5 mL; a melting temperature of at least about 87xc2x0 C.; a latent heat of at least about 5 joules/g; a ratio of sodium ions to a total amount of sodium, calcium and potassium ions of no more than 0.5; no more than about 7000 mg/kg (dsb) sodium ions; and a bacteria load of no more than about 50,000 cfu/g.